Among backlights that are assembled into liquid crystal display devices, there are backlights of a bifacial light emitting type, which emit light from both faces of a light guide plate. Conventional bifacial light emitting backlights are provided with a large number of optical sheets (a lens sheet, a diffusion sheet, or the like) in each of the both faces of the light guide plate. Thus, there arise problems such as difficulty in achieving a slim backlight, requiring cost for the number of optical sheets, and resulting in increased cost due to increased production processes.
Thus, Patent Document 1 discloses a bifacial light emitting backlight in which an emitted-light control plate having microstructure prism arrays formed in one face thereof is in close contact with each of both faces of a light guide plate. Such a bifacial light emitting backlight makes it possible to reduce the number of optical sheets, and thus to achieve slim backlights and to reduce cost.    Patent Document 1: JP-A-2002-133906